1. Field of the Invention
The present invention relates to a converting circuit for a sampling phase of digital data.
2. Description of the Related Art
In home-use VTRs, for instance, an 8-mm video recorder, a luminance signal is converted into an FM signal SY during a recording operation (see FIG. 6). Further, a carrier color signal SC is frequency-converted into a lower band side of the FM luminance signal, and an audio signal is converted into an FM signal SA in a band between the signal SC and the signal SY. Then, a frequency multiplexed signal SF produced from these signals SY, SC, SA and a tracking servo pilot signal SP is recorded on a magnetic tape by way of a rotary magnetic head in such a manner that a 1-field signal SF becomes one inclined magnetic track on this magnetic tape.
As a consequence, this signal reproducing system may be arranged as shown in, for example, FIG. 7. That is, the frequency multiplexed signal SF is continuously reproduced from the magnetic tape 1 by the rotary magnetic heads 11A and 11B. The reproduced signal SF is supplied via the reproducing amplifier 12 to the servo circuit 41, so that the tracking servo control for the heads 11A and 11B with respect to the tracks of the magnetic tape 1 is carried out in response to the pilot signal SP contained in the signal SF.
Also, the signal SF derived from the amplifier 12 is supplied to the bandpass filter 13 so as to derive the FM luminance signal SY. This FM luminance signal SY is supplied to the A/D converter 14 in order to be A/D-converted into, for instance, an 8-bit digital signal for 1 sample, whose sampling frequency is eight times higher than the color subcarrier frequency fSC (approximately 3.58 MHz). Then, this 8-bit digital signal SY is supplied to the processing circuit 15 in which such process operations as FM demodulation and deemphasis are carried out. Then, the processed signal SY is supplied to the D/A converter 16 so as to be D/A-converted into the original baseband luminance signal Y which will then be derived from the terminal 17.
Furthermore, the signal SF derived from the amplifier 12 is supplied to the bandpass filter 21, thereby deriving the color carrier signal SC. This color carrier signal SC is supplied to the A/D converter 22 so as to be A/D-converted into, for instance, an 8-bit digital signal SC for 1 sample, having a sampling frequency four times higher than the color subcarrier frequency.
Then, this 8-bit digital signal SC is supplied to the processing circuit 23 so that such processing operations as APC and eliminations of track crosstalk components are carried out, and this digital signal SC is color-demodulated into the baseband red and blue color difference signals (R-Y) and (B-Y). These color difference signal (R-Y) and (B-Y) are supplied via the converting circuit (will be discussed later) 24 to the NTSC encoder 25 in which the color subcarrier frequency is encoded into the color carrier signal SS having the frequency fSC. This color carrier signal SS is supplied into the D/A-converter 26 so as to be D/A-converted into the original color carrier signal SS, which will then be derived from the terminal 27.
At this time, both of the luminance signal Y derived from the D/A converter 16 and the color carrier signal SS derived from the D/A converter 26 are supplied to the adding circuit 18, so that the NTSC composite signal is synthesized which will then be derived from the terminal 19.
Moreover, the signal SF from the amplifier 12 is furnished to the audio processing circuit 31, so that the original audio signals "L" and "R" are demodulated from the FM audio signal SA contained in this signal SF. These original audio signals are derived from the terminal 32.
In the above-described signal reproducing system, both of the reproduced FM luminance signal SY and color carrier signal SC contain variations in a time axis such as "jitter". Also, the time axis is changed when the VTR signal is reproduced at varied speeds. As a consequence, when the various signal processing operations are carried out in the processing circuits 15 and 23, the clock thereof is produced from the horizontal sync signal contained in the reproduced FM luminance signal SY. Then, as a result, various variations are produced in the sampling phases (namely, phase at time instant when data is obtained) among the luminance signals Y outputted from the processing circuits 15, 23, and the color difference signals (R-Y), (B-Y) outputted from the processing circuit 23.
Therefore, the circuit for stabilizing the sampling phases and for aligning the sampling phases of the color difference signals (R-Y) and (B-Y) derived from the processing circuit 23 is the converting circuit 24. That is to say, the converting circuit 24 is to convert the sampling phases of the color difference signals (digital data) derived from the processing circuit 23 into the clock phases of the encoder 25 even when the processing circuit 23 is operated in a synchronism with the encoder 25.
In the signal reproducing system of FIG. 7, the signal recording system similarly requires such a converting circuit for stabilizing and aligning the sampling phases in the digital processing circuit for the color carrier signal due to the same jitter reason.
The present invention has an object to provide a novel converting circuit for converting such a sampling phase of digital data. More specifically, the present invention has another object to provide a converting circuit with a simple structure, whose characteristic is better than that of the conventional converting circuit.